1. Field of the Invention
The present invention relates to a hold-down structure for use in a corrugated board making machine and more particularly, to such a hold-down structure, which positively compact the whole area of the workpiece.
2. Description of the Related Art
Under the emerging environment protection trend, paper is intensively used for packing different products. For the advantages of strong, durable, shockproof and easy-to-print characteristics, corrugated board is a good material for making packing boxes. Corrugated board is classified, according to the number of outer/intermediate plies and flutes: single face corrugated board consists of one ply of fluted paper, onto which paper is glued; single wall (double face) corrugated board consists of one ply of fluted paper which is glued between two plies of paper; double wall corrugated board consists of two plies of fluted paper which are glued together by one ply of unfluted paper and the exposed outer surfaces of which are each covered with one ply of paper; tri-wall corrugated board consists of three plies of fluted paper which are glued together by two plies of paper and the outer surfaces of which are likewise each covered with one ply of paper.
During fabrication of a corrugated board, a hold-down structure is used to apply a pressure to the processed corrugated board, compacting the structure. FIG. 8 illustrates a hold-down structure used in a corrugated board making machine. According to this design, the hold-down structure comprises a circulating endless lower transfer belt A1, a circulating endless upper transfer belt A2 spaced above the circulating endless lower transfer belt A1, a transfer path A3 defined between the circulating endless lower transfer belt A1 an the circulating endless upper transfer belt A2 through which the processed corrugated board B is transferred, and a plurality of pressure rollers A4 arranged in parallel and pressed on the top surface of the lower part of the circulating endless upper transfer belt A2 to give a pressure to the processed corrugated board B that is being transferred through the transfer path A3. According to this design, the pressure rollers A4 are cylindrical rollers arranged in parallel and spaced from one another at a certain distance. When the processed corrugated board B is being transferred through the transfer path A3, it receives pressure from the pressure rollers A4 at spaced locations, i.e., the applied pressure is not evenly distributed through the processed corrugated board B, affecting the bonding tightness between the plies and flutes. Further, this design does not allow the worker to adjust the applied pressure subject to actual requirements.